Nuclear transplantation studies of nuclear differentiation: Nuclei of somatic cells show stabilized cell-type specific patterns of gene expression. We propose to determine whether this stabilization is a property of the nucleus, the cytoplasm, or both by transplanting somatic nuclei into oocytes. Genetic markers now available in the axolotl include genes normally active in oocytes and inactive in most somatic cells (e.g. the gene for melanin synthesis), and genes active in certain somatic cells and not in oocytes (e.g. the gene for ADH in liver). Thus both positive and negative changes in gene activity can be detected when somatic nuclei are transplanted into oocytes. Genetic control of organogenesis: Another long-standing problem concerns the nature of inductive interactions leading to the development of embryonic organs. Genes are known which block the development of the heart (c) and eye (e) in the axolotl. The c gene affects the inducing tissue (endoderm) for heart formation; the e gene affects the competence of the eye-forming ectoderm to respond to induction by chorda-mesoderm. Further analysis of the inductive interactions in normal and mutant embryos is proposed, particularly induction leading to eye formation. BIBLIOGRAPHIC REFERENCES: Briggs, R. 1977. Genetics of cell type determination. In press in "Cell Interactions in Differentiation." Academic Press. Humphrey, R.R. 1977. Factors influencing ovulation in the Mexican axolotl as revealed by induced spawnings. In press, J. Exp. Zool.